1. Field of the Invention
The present invention relates to a method for producing a silicon single crystal which facilitates a production of silicon single crystals which show, throughout the entire length of the crystal, small heterogeneity in radial distribution of crystal defects and provides a radial section entirely composed of a single type crystal defect region. The invention also relates to a silicon single crystal produced by the same method Priority is claimed on Japanese Patent Application No. 2005-214236, filed Jul. 25, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
A silicon single crystal may be produced through the Czochralski method (CZ method) in which a silicon single crystal is grown by pulling the silicon single crystal from a silicon melt In the CZ method, a polycrystalline silicon raw material is charged in a crucible, and is heated to a molten state by a heater, thereby forming a silicon melt. Subsequently, a silicon single crystal may be grown by pulling the silicon single crystal from the silicon melt. A silicon substrate may be produced by slicing a silicon single crystal produced by the above-described method. Along with the recent trend of downsizing semiconductor elements in accordance with development of highly integrated semiconductor circuits, there is an increasing demand for quality-improvement of silicon single crystals as a substrate of semiconductor circuits.
Conventionally, a pulling method using an applied magnetic field (MCZ method) is known as a method for suppressing silicon melt convection and for providing a homogeneous silicon single crystal (e.g., Patent Reference 1: Japanese Unexamined Patent Application, First Publication, No.S64-24090).
As s a well known phenomena, a silicon single crystal produced by a conventional CZ method comprises a plurality of types of crystal defect regions including: an interstitial silicon-type point defect region (hereafter referred to as I region ) in which interstitial silicon (silicon atom as interstitial atom)-type point defects dominantly occur; a vacancy-type defect region in which vacancy-type point defects dominantly occur and aggregates of vacancy-type point defects occur (hereafter referred as V region); a perfect region (hereafter referred to as P region) in which aggregates of interstitial silicon-type point defects and aggregates of vacancy type point defects do not occur; a region (hereafter referred as OSF region) in which nuclei of oxidation induced stacking fault (OSF) occur. The OSF region occurs between P region and V region and shows a ring-like distribution in a section perpendicular to a direction of crystal growth.
Controlling of the growth conditions of a silicon single crystal has been proposed as a method for producing a silicon single crystal from which a radial section entirely composed of a P type region can be obtained (e.g., Patent Reference 2; Japanese Unexamined Patent Application First Publication, No. 2000-154093).
However, in the technique of Patent Reference 2, because of the very narrow range of preferable conditions such as pulling rate and thermal gradient, it has been difficult to control the conditions to obtain a defect-free crystal. Such difficulty causes a problem in practical production of defect-free crystals. The technique of Patent Reference 1 has an objective of increasing the oxygen concentration in a silicon single crystal without reducing the pulling rate of the crystal. By the technique of Patent Reference 1, it is impossible to pull a silicon single crystal radial section of which is entirely composed of a single type of defect region.
In view of the abovedescribed circumstances, an object of the invention is to provide a method for producing a silicon single crystal, which facilitates the production of silicon single crystals, throughout the entire length thereof, showing small heterogeneity in radial distribution of crystal defects and providing a radial section entirely composed of a single type crystal defect region. The invention also aims to realize a silicon single crystal produced by the same method which shows a radial section entirely composed of a single type crystal defect region.